Inorganic porous body and method for producing the same

ABSTRACT

This invention aims to provide an inorganic porous body which can be ensured with high strength and high porosity and which is applicable to soil conditioners. The inorganic porous body has a pellet-shape having pores, includes 50% and more silica by weight, and 20% and more alumina by weight. Also, the inorganic porous body has a porosity of 40% and more by volume. The sludge, which discharged from casting foundries as sludge-wastes and which has an ignition loss of 20%, is utilized as a starting material. The starting material is mixed with water to make a mixture, the mixture is formed to become pellets, and the pellets are burned.

This is a division of application Ser. No. 08/760,765, filed on Dec. 5,1996, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an inorganic porous body having pores and amethod for producing the same. The present invention is applicable to,for instance, soil conditioners to be buried in the ground for holdingwater.

2. Description of the Related Art

Dust, discharged from casting foundries as industrial wastes, includes alarge amount of carbon capable of working as a pore-forming substance.In view of such, there has been recently proposed a technique in whichdust is utilized to be transformed into an inorganic porous body(Niigata Industrial Technique Center: 1992, Research Report No.21).

According to this technique, dust discharged from casting foundries asindustrial wastes is utilized as a starting material. After the startingmaterial is wet-kneaded, a continuous extrusion long-body is formed byuse of a extrusion machine. Thereafter, the extrusion long-body is cutat intervals in the longitudinal direction to become a lot ofcylindrical pellets having a diameter of approximately 1 mm. Next, thepellets are dried and burned in high temperature regions to transforminto inorganic porous bodies. Since this technique can effectivelyutilize the dust discarded as wastes, it has been promising recently.

Now, according to the inorganic porous body produced by use of theaforementioned technique, the higher strength is, the lower porosity is.Also, the higher porosity is, the lower strength is. Namely, highstrength and high porosity are liable to be opposed to each other.

Here, the aforementioned inorganic porous body can be utilized as soilconditioners to be buried in the ground. Even when the inorganic porousbody is utilized as soil conditioners, a similar phenomenon isgenerated. Namely, as for the inorganic porous body, it is preferablethat porosity is high for improving water-holding capacity in theground; however, strength is so lower that the inorganic porous body iseasy to be destroyed and pulverized to be short-lived easily.

On the other hand, when porosity of the inorganic porous body is lower,the inorganic porous body is improved in strength, foot-pressureresistance, and weathering-resistance to be long-lived; however,water-holding capacity of the inorganic porous body is lower and thefunction working as soil conditioners deteriorates in holding water.

Moreover, according to the aforementioned technique, as mentioned above,after the continuous extrusion long-body is formed by use of theextrusion machine, the continuous extrusion long-body is out atintervals in the longitudinal direction by use of a cutter to become alot of cylindrical pellets, and the pellets are dried and burned.Therefore, in this cut-method, "drooping portions" are easy to occur ina cut surface, so that "drooping portions" may project locally toconstitute edge-portions. In this case, it is thought that theedge-portions are easy to be destroyed and strength property such asfoot-pressure resistance isn't sufficient even when the inorganic porousbody is burned.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the abovecircumstances. It is an object of the present invention to provide aninorganic porous body which can ensure strength advantageously withporosity thereof being high and which is suitable to be utilized as soilconditioners to be buried in the ground.

It is another object of the present invention to provide a method forproducing an inorganic porous body which can ensure strengthadvantageously with porosity thereof being high and which is suitable tobe utilized as soil conditioners to be buried in the ground.

(1) The present inventors have studied about an inorganic porous body inthe long term. As a result, in the case where alumina content in aninorganic porous body is large, the inventors have found that strengthof the inorganic porous body is liable to increased with porositythereof being high, so that they have developed the inorganic porousbody of the first aspect of the present invention.

The reason why a large amount alumina content cause strength to beimproved in the inorganic porous body isn't clear. However, it isguessed as follows: Although burning in high temperatures is preferableso as to improve strength of the inorganic porous body, liquidus phasesmay considerably occur undesirably. In such a case, pores of theinorganic porous body are filled owing to solidification of the liquidusphases, and thereby porosity is easy to be decreased considerably. Onthe other hand, when the burning temperature is suppressed low, burningability isn't ensured sufficiently and strength of inorganic) porousbody is easy to be decreased. This may be caused by the fact thatburning in high temperatures can be carried out while suppressingliquidus phases from occurring, in case where alumina content in theinorganic porous body is in a large amount.

Here, with consideration that alumina content in silica-sand whichrepresents casting sand is in the range of from 7 to 8%, and silicacontent in the silica-sand is in the range of from 87 to 99% ( referencebook: Standard Metal Engineer Course "Casting", 40 page, by publishedCorona Co., Ltd. the thirteenth edition), it is thought that the aluminacontent in the inorganic porous body concerning the aforementionedresearch report proposed by Niigata Industrial Technique Center is lowto be 10% at the most. Here, the word of "%" herein means wt % unless itis described as volume %.

Moreover, the present inventors have found sludge-wastes discharged fromcasting foundries includes minute colloidal particles in a considerableamount so that minute particles are included in the sludge-wastes in alarge amount. Also, they have found the sludge-wastes includes a largeamount of organic substances to be burned during a burning step thangeneral dust-wastes. Accordingly, they have found that strength ofinorganic porous body can be increased with porosity thereof providedthat sludge obtained from the sludge-wastes is utilized as a startingmaterial. On the basis of this finding, they have developed the thirdaspect of the method according to the present invention.

Still further, provided that not the aforementioned cut-method forcutting the continuous extrusion long-body to obtain a lot of pelletsbut a friction-rolled method utilizing friction between a startingmaterial and a stirring wing for obtaining pellets is employed, thepresent inventors have found that edge-portions of the inorganic porousbody are decreased and the inorganic porous body strengthens withporosity thereof being high, even when the dust-wastes discharged fromcasting foundies is utilized as a starting material in the same way asthe aforementioned conventional "Niigata" technique.

On the basis of this finding, the present inventors have developed thethird aspect of the present invention.

(2) In the first aspect of the present invention, an inorganic porousbody is characterized in that: it has a pellet-shape possessing pores,includes 50% and more silica by weight, and 20% and more alumina byweight; and it has a porosity of 40% and more by volume.

On average, the pore-diameter of inorganic porous body can be set from0.1 to 20 um (micro meters), in particular, from 1 to 5 um(micrometers). The porosity of the inorganic porous body can be set in therange of from 50 to 70%.

In the second aspect of the present invention, an inorganic porous bodymay have a non-cylindrical shape.

In the third aspect of the present invention, a method for producing aninorganic porous body uses a staring material which has an ignition lossof 20% and more by weight and in which sludge is utilized as a mainconstituent, the sludge includes silica and alumina discharged from acasting foundry as sludge-wastes,

and comprises the steps of:

forming a pellet-shaped body or a lump-shaped body from a mixture mixingsaid starting material with water, and

heating said pellet--shaped body or said lump-shaped body in the rangeof 900° C. and more to burn said pellet-shaped body or said lump-shapedbody, thereby constituting the inorganic porous body.

The ignition loss means the loss to be burned owing to high-temperatureheat during a burning step, it mainly exhibits an amount of organicsubstances to be burned owing to high-temperature heat, and it doesn'tinclude water.

In the third aspect of the present invention, the sludge working as thestarting material can include from 8 to 40% alumina by weight, and 50%and more silica by weight, except for parts which corresponds to theignition loss. Also the sludge can include from 18 to 40% alumina byweight, and from 50 to 70% silica by weight. The particles constitutingthe sludge can have a median diameter of 0.1 to 20 um (micro meters),and a mode diameter of 0.1 to 20 um (micro meters),

In the fourth aspect of the present invention, a method for producing aninorganic porous body uses a staring material which has an ignition lossof 10% and more and in which dust is utilized as a main constituent, thedust includes silica and alumina discharged from a casting foundry asdust-wastes,

and comprises the steps of:

mixing the starting material with water to make a mixture by means of astirring wing, thereby forming a pellet-shaped body having anon-cylindrical shape, and

heating the pellet-shaped body in the range of 900° C. and more to burnthe pellet-shaped body, thereby constituting the inorganic porous body.

The dust working as the starting material can include from 9 to 40%alumina, and 50% and more silica (generally, from 50 to 85% silica) byweight, except for parts which correspond to the ignition loss. Theparticles constituting the dust can have a median diameter of 1 to 50 um(micro meters), and a mode diameter of 1 to 50 um (micro meters),

In the fifth aspect of the present invention, the staring materialincludes carbon-based powder, an average particle-diameter of thecarbon-based powder may be larger than an average particle-diameter ofparticles constituting the sludge. Also, an average particle-diameter ofthe carbon-based powder may be larger than an average particle-diameterof the particles constituting the dust. The average particle-diameter ofcarbon-based powder can be set in the range of from 2 to 100 um (micrometers).

In the first aspect of the present invention, the inorganic porous bodyhas a pellet-shape possessing pores, includes 50% and more silica byweight, and 20% and more alumina by weight; and it has a porosity of 40%and more by volume. Therefore, strength of the inorganic porous body canadvantageously be ensured with porosity thereof being high. Suchinorganic porous body has high porosity to obtain a water-holdingproperty. Also, since such inorganic porous body has strength,destruction-resistance thereof is high. This may be caused by the factthat alumina content is rich in the inorganic porous body. Accordingly,the inorganic porous body of the present invention is suitable for usingin floriculture, horticulture, tree-planting, agriculture, cultivation,and the like.

In the second aspect of the present invention, the inorganic porous bodyis a pellet having a non-cylindrical shape, therefore, edge-portionsoccurring is suppressed as distinct from the conventional cylindricalshaped inorganic porous body having a tendency for the edge-portions tooccur because of cutting with a cutter. As a result, the inorganicporous body is improved in fracture-resistance and life. When theinorganic porous body is used as soil conditioners to be buried in theground, foot-pressure resistance can be improved.

In the third aspect of the present invention, the sludge, which includesa large amount of organic substances having a tendency to be burnedbecause of heat during a burning step, is utilized as a mainconstituent. Therefore, the ignition loss of the starting material canbe set at 20% and more by weight, and the porosity of the inorganicporous body can be increased. The reason is that portions correspondingto the ignition loss are burned and disappeared to become poressubstantially during the burning step. Thus, when the inorganic porousbody is used as soil conditioners to be buried in the ground, awater-holding property can be improved.

Moreover, in the third aspect of the present invention, as the startingmaterial, the sludge, including silica and alumina discharged fromcasting foundries, is utilized. As for the sludge, dry-sludge removingwater is preferable. Since the sludge includes a large amount of minuteparticles of alumina and silica, burning ability of the sludge isimproved, and burned strength of the inorganic porous body canadvantageously be increased with porosity thereof being high. As aresult, the inorganic porous body is improved in fracture-resistance andlife. When the inorganic porous body is used as soil conditioners to beburied in the ground, foot-pressure resistance of the inorganic porousbody is more improved. When the inorganic porous body is lump-shaped, itcan be utilized as a block. In such a case, the durability of block canbe improved.

Further, in the third aspect of the present invention, twoconfigurations are usable for constituting the pellet-shaped body. Inone configuration, the mixture mixing the starting material with wateris stirred by the stirring wing to become a pellet-shaped body by use ofthe friction between the stirring wing and the starting material. Inanother configuration, the continuous extrusion long-body formed of themixture is cut at intervals by use of a cutter to become a lot ofpellet-shaped bodies. In the former, edge-portions owing to "droopingportions" occur rarely, so that strength of the inorganic porous bodycan be more ensured with porosity thereof being high; thus, theinorganic porous body is improved in foot-pressure resistance property,and it is suitable for using as soil conditioners.

In the fourth aspect of the present invention, the dust is utilizedwhich is discharged from casting foundries have an ignition loss of 10%and more by weight. Therefore, porosity can advantageously be high withstrength being ensured. The reason is that portions corresponding to theignition loss become pores substantially.

Moreover, in the fourth aspect of the present invention, since thenon-cylindrical shaped pellet is formed, the occurrence of theedge-portions owing to "drooping portions" can be suppressed, asdistinct from the conventional technique in which the continuousextrusion long-body is cut at intervals so as to obtain cylindricalpellets. As a result, strength of the inorganic porous body canadvantageously be increased with porosity thereof being high.

In fifth aspect of the present invention, carbon-based powder (coalpowder, activated carbon powder, graphite powder and the like) is burnedand disappeared during the burning step to work as a pore-formingsubstance, and thereby porosity of the inorganic porous body is liableto be ensured.

Further, the average particle-diameter of the carbon-based powder islarger than the average particle-diameter of the particles constitutingthe sludge, or the average particle-diameter of the particlesconstituting the dust; therefore, porosity of the inorganic porous bodycan advantageously be more improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be shown and described in terms ofconcrete embodiments thereof with reference to the appended drawings, inwhich:

FIG. 1 is a graph showing a particle-diameter distribution of particlesof sludge;

FIG. 2 is a graph showing a particle-diameter distribution of particlesof dust;

FIG. 3 is a constitutional view of a kneading machine for formingpellets;

FIG. 4 is a perspective view showing representative configurations of aninorganic porous body;

FIG. 5(A) is a graph showing pore-diameter distribution concerningExamples 1,2;

FIG. 5(B) is a graph showing pore-diameter distribution and coal powderparticle-diameter distribution concerning Examples 1,2;

FIG. 6(A) is a graph showing pore-diameter distribution concerningExamples 3,4;

FIG. 6(B) is a graph showing distribution and coal powderparticle-diameter concerning Examples 3,4;

FIG. 7(A) is a graph showing pore-diameter distribution concerningExample 5;

FIG. 7(B) is a graph showing pore-diameter distribution concerningExample 5; and

FIG. 8 is a graph showing result in a strength test of an inorganicporous body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The First PreferredEmbodiment

In the present embodiment, sludge, discharged from casting foundries assludge-wastes, is utilized as a starting material. In the presentembodiment, the sludge-Wastes, accumulated at a drainage of castingfoundries, are filtrated by use of a filter-pressing machine, andsludge-wastes are dried by use of sunlight and heat-treatment to becomecake-shaped. In such a way, the sludge-cakes concerning the presentembodiment are obtained.

In the aforementioned sludge-wastes, various mud is mixed. For instance,watery-mud including dust discharged from production-lines in castingfoundies, and watery-mud constituted by livelihood sludge-waterincluding sewage-water discharged from dining rooms and toilets incasting foundries. Thus, a large amount of organic substances areincluded in the sludge-wastes, and they are burned and disappeared inburning step; the ignition loss is large in the sludge-wastes.

FIG. 1 shows an example in particle-diameter distribution aboutparticles constituting the sludge utilized in the First PreferredEmbodiment. In FIG. 1, the horizontal axis shows particle-diameter ofthe particles constituting the sludge, and the vertical axis showsrelative particle amount (wt %). As shown in FIG. 1, the particlesconstituting the sludge had a median diameter of 3.365 um (micro meters)and a mode diameter of 3.176 um (micro meters). In such a manner, theparticles constituting the sludge are easy to become minute. Here, themedian diameter means the central value in diameter, and the modediameter means the most frequent diameter. The median diameter and themode diameter work as the average-diameter.

The sludge includes more than 50% by weight of silica, and more than 20%by weight of alumina. Therefore, the sludge has so highly aluminacontent that an inorganic porous body having high-strength can beadvantageously produced.

In the present Embodiment, the aforementioned sludge-cakes are dried,and thereafter they are crushed minutely.

Further, the crushed sludge-cakes are disposed in a kneading machine 10illustrated schematically in FIG. 3(A). The crushed sludge-cakes areproperly mixed with water to become 10 to 30% by weight of water, andthey are kneaded by use of the kneading machine 10 to be transformedinto a mixture. Here, the phrase of "10 to 30% by weight of water" meansthat water is included 10 to 30%, when the mixture included the startingmaterial sludge and the water is 100%.

Utilizing the method mixing dried sludge-cakes with water can beadvantageous in adjusting water content of the mixture and in ensuringpelletization. From this regard, dried sludge-cakes are advantageous assludge.

The kneading machine 10 illustrated in FIG. 3 has a container 11, arotating shaft 12, a motor 13, and a plurality of stirring wings 14. Thecontainer 11 having the bottom is inclined with respect to thehorizontal line, and it is capable of receiving the starting materialand capable of rotating in the direction of the arrow X1. The rotatingshaft 12 is capable of rotating in the direction of the arrow X2, themotor 13 is capable of rotating the rotating shaft 13, and the stirringwing 14 is held on the the rotating shaft 13 in the container 11.

FIG. 3 (B) shows the stirring wing 14 schematically. As shown in FIGS.3(A)(B), the stirring wing 14 comprises a plurality of plate-shapedwings 14i. The rotation of the plate-shaped wings 14i rolls the startingmaterial thereunder to pelletize a lot of pellets gradually, therebygrowing pellets "W".

Perhaps the pelletization progresses as follows: Since the plate-shapedwings 14i are inclined with respect to the bottom of the container 11,grains with solid-mass work as nucleuses. The nucleuses are pressedagainst the starting material piled up on the bottom of the container11, so that the pelletization of pellets "W" progress. In the FirstPreferred Embodiment, the starting material is pelletized to become alot of raw pellets "W" having a diameter of, for example, 0.3 to 20 mm.In the First Preferred Embodiment, pellets "W" may be set over 20 mm or30 mm in a diameter.

Generally, in the pelletization, shortening the pelletizing time ispreferable for decreasing a pellet-diameter, and elongating thepalletizing time is preferable for increasing a pellet-diameter. Thepellets "W", produced on the basis of the aforementioned process, areheated and held at a temperature of 140° C. for 60 minutes fordry-treatment, and thereby water is removed from the pellets "W".Thereafter, the pellets "W" are burned at 1000° C. for over 30 minutesin the atmosphere, and thereby a plurality of the inorganic porousbodies are constituted. As schematically illustrated in FIG. 4, theinorganic porous body "Wa" constitutes a pellet having an oval-shape.

When burning temperature is too high, liquidus phases occur excessively,and porosity of the inorganic porous body is liable to be decreased inspite of the fact that strength thereof is improved. Therefore, heatingat the excessive high burning temperature isn't desirable. In the FirstPreferred Embodiment, the ignition loss of the starting material is over20%. The ignition loss means the weight-loss resulting from burning inhigh temperatures with respect to the state in which water is removedowing to dry-treatment. In the First Preferred Embodiment, after thetest specimen is dried at 140° C. for 60 minutes for removing water. Theweight of the test specimen is measured as "W1". Also, after the testspecimen is burned, the weight of the test specimen is measured as "W2".Provided that the difference between "W1" and "W2" in weight isexhibited as "(delta)W", the ignition loss is calculated as follows:

    ignition loss={ (delta)W!/ W1!}×100%

The sludge includes numerous organic substances which are burned downand disappeared because of heating during the burning step; therefore,the ignition loss is large. In such sludge, the ignition loss is liableto vary depending on sludge-collecting locations. Thus, as for theignition loss of the starting material, 20% or more, 25% or more, 30% ormore, and 35% or more may be utilized.

The inventors have measured the aforementioned inorganic porous bodyafter the burning step, the porosity thereof was 50% or more, 60% ormore, and 65% or more. This results may be caused by the fact thatpore-volume increases because the ignition loss is large in the startingmaterial. Since the sludge-wastes constituting the sludge includeslivelihood sludge-water in which the organic substances to be burneddown come to be rich, porosity of the inorganic porous body is easy tobe ensured.

Here, the porosity is calculated by volume, namely, it is calculated asfollows:

    porosity=(pore-volume of inorganic porous body)/(apparent volume of inorganic porous body)×100%

Table 1 shows sludge-composition before and after burning, the ignitionloss, and the porosity of the inorganic porous body constituted from thesludge, as an example.

Table 1!

The composition analysis results shown in Table 1 is carried out by useof fluorescence X-ray method. The composition shown in Table 1 doesn'tinclude parts which corresponds to the ignition loss in before and afterburning. This is similar to Tables 2,3 described later.

Table 2 shows the sludge-compositions before and after the burning, theignition loss, and the porosity of the inorganic porous body constitutedfrom the sludge in which is collected at the same locations as that ofTable 1 at different days. Table 2 indicates that the sludge includes20% and more alumina by weight; therefore, strength of the inorganicporous body after the burning is advantageously increased. Also, sincethe ignition loss of the sludge was more than 20% to become high, theporosity of the inorganic porous body after the burning isadvantageously ensured. In this connection, as understood in Table 2,the porosity of the inorganic porous body was 48% or more.

Table 2!

In Tables 1 and 2, the ratio of (alumina/silica) is in the range of from0.3 to 0.6. The ratio may be set in the range of from 0.1 to 1.

According to the First Preferred Embodiment, burning temperature can beselected depending on kinds of the starting material, the suppressing ofa liquidus phase in occurrence is preferable in order to increaseporosity of the inorganic porous body. On the other hand, the occurringof a liquidus phase increases strength of the inorganic porous bodyprobably.

However, in order to increase porosity, burning temperature not togenerate a liquidus phase is preferable. Also, even when a liquidusphase occurs, burning temperature is preferable in a region where littleliquidus phase occurs. In view of such circumstances, in accordance withkinds of the starting material. The upper limit of the burningtemperature can be set at 1000° C., 1050° C., 1100° C., and 1200° C.;the lower limit of the burning temperature can be set at 800° C., 850°C., 900° C., and 950° C., These options in temperature are similar inthe other Embodiments.

In the First Preferred Embodiment, not only a pellet body but also alump body or a bulky body may be formed as a inorganic porous body.

Second Preferred Embodiment

The Second Preferred Embodiment is substantially the same as the FirstPreferred Embodiment in construction except for coal powder. Namely, inthe First Preferred Embodiment, the sludge which doesn't include coalpowder is utilized as the starting material. On the other hand, in theSecond Preferred Embodiment, sludge utilized as a starting materialincludes coal powder working as carbon-based powder.

In accordance with the Second Preferred Embodiment, the coal powder tobe burned and disappeared during the burning step is included in thestarting material in addition to the sludge including organicsubstances. Therefore, the ignition loss is liable to be increased more.Accordingly, the ignition loss of the starting material concerning theSecond Preferred Embodiment exceeds 24% or 30% sometimes. Also, it canexceed 35% in accordance with kinds of sludge and coal powder.

Use of the starting material having a large amount of ignition lossallows the porosity of inorganic porous body to be ensured largely. Theporosity can be expected to exceed 40%,45%,50%,60%, and 65% inaccordance with kinds of the starting material.

In the Second Preferred Embodiment, the average particle-diameter of thecoal powder is larger than that of particles constituting the sludge.

Third Preferred Embodiment

The Third Preferred Embodiment is substantially the same as the FirstPreferred Embodiment in construction except for a starting material.Namely, the Third Preferred Embodiment is different from the FirstPreferred Embodiment in that the dust, discharged as dust-wastes fromdust-collectors of casting foundries for producing (cast iron, isutilized as a starting material.

FIG. 2 shows particle-diameter distribution of the dust utilized in oneexample of the Third Preferred Embodiment. The horizontal axis of FIG. 2shows particle-diameter of the dust, and the vertical axis thereof showsa relative particle amount(wt %). As shown in FIG. 2, inparticle-diameter, the particles constituting the dust had a mediandiameter of 7.652 um (micro meters) and a mode diameter of 13.711 um(micro meters). As understood from comparison between. FIG. 1 concerningthe sludge and FIG. 2 concerning the dust, the dust had a lot ofparticles whose particle-diameter is larger than particle-diameter ofthe sludge; to put it concretely, there are a lot of dust-particleshaving a diameter exceeding 10 um (micro meters) in the presentEmbodiment.

This dust includes 50% or more silica and 10% or more alumina by weight.No.1A and No.2A in Table 3 show the dust-composition as examples beforeburning step. Also, Table 3 shows the ignition loss, and the porosity ofthe inorganic porous body constituted from the dust.

As understood in Table 3, in the dust utilized in the Third PreferredEmbodiment, alumina content and ignition loss of the dust are decreasedas compared to those of the sludge. It is thought that the ignition lossof the dust is decreased as compared to that of the sludge, because thedust comes from casting sand for casting high-temperature melt to beheated during casting.

Table 3!

Test Examples

1. Example 1, Example 2

In Example 1, sludge, which doesn't include coal powder, is utilized asa starting material, and thereby an inorganic porous body is formed onthe basis of the method of the First Preferred Embodiment. In Example 1,particle-diameter distribution of particles in the sludge is the same asresults shown in Table 1. Also, the composition of the sludge working asthe starting material, the ignition loss, and so on are the same as theresults shown in Table 1. In the Example 1, the burning temperature was1000° C., the burning time was 120 minutes, the porosity of theinorganic porous body was 51%.

In Example 2, sludge including coal powder is utilized as a startingmaterial, an inorganic porous body is formed on the basis of the methodof the Second Preferred Embodiment. As for the starting materialconcerning Example 2, coal powder:sludge =1:10 by weight. Thus, amixture is adjusted to has 20% water. Characteristic Line K3 in FIG.5(B) indicates the grading degree of the coal powder.

Particle-diameter distribution of particles in the sludge concerningExample 2 is basically the same as that of the First PreferredEmbodiment. Also, the composition of the sludge working as the startingmaterial, the ignition loss, and so on are the same as the those ofExample 1. In the Example 2, the burning temperature was 1000° C., theburning time was 120 minutes, the porosity of the inorganic porous bodywas 67%.

The inventors have measured the pores of the inorganic porous body afterthe burning step in both of Example 1 and Example 2. In measurement, aporosimeter (made by Simazu-Micromeritix Co., Ltd.) havingmercury-inserting method was utilized. After the test specimen wasimmersed in mercury, the mercury was pressed to insert the pores of thetest specimen; pores distribution is measured on the basis of a mercuryamount inserted into the test specimen and a pressure value measuredwith the porosimeter. FIGS. 5 (A)(B) shows measured results. Thehorizontal axis in FIG. 5(A) shows pore-diameter of the inorganic porousbody; the vertical axis in FIG. 5(A) shows pore-volume of the inorganicporous body. Characteristic Line H1 in FIG. 5(A) shows pores-volumescumulated from the small side of pore-diameter in the inorganic porousbody concerning Example 1 in which the sludge working as a startingpowder doesn't include coal powder. Characteristic Line H2 in FIG. 5(A)shows pores-volumes cumulated from the small side of pore-diameter inthe inorganic porous body concerning Example 2 in which the sludgeworking as a starting powder includes coal powder.

The horizontal axis in FIG. 5(B) shows pore-diameter of the inorganicporous body and particle-diameter of the coal powder; the left side ofthe vertical axes shows differentiated value of the characteristic linesillustrated in FIG. 5(A), that is, an inclination of the characteristiclines illustrated in FIG. 5(A). The right side of the vertical axesshows a grading ratio of the coal powder.

Characteristic Line K1 in FIG. 5(B) shows pores-diameter distribution ofthe inorganic porous body concerning Example 1 in which the sludgeworking as a starting powder doesn't include coal powder. As shown byCharacteristic Line K1 in FIG. 5(B), the maximum frequency region ofpores-diameter was 3 to 4 um (micro meters) in Example 1.

Characteristic Line K2 in FIG. 5(B) shows pore-diameter distribution inthe inorganic porous body concerning Example 2 in which the sludgeworking as a starting powder includes coal powder. As shown byCharacteristic Line K2 in FIG. 5(B), the maximum frequency region ofpores-diameter was 3 to 4 um (micro meters) in Example 2. In this way,the pore-diameter concerning Example 1 was similar to the pore-diameterconcerning Example 2 in the maximum frequency region. Probably, thisreason is that the inorganic porous body contracts during the burningstep and the contraction influences that results. Also, a peak ofCharacteristic Line K2 is higher than that of the Characteristic LineK1.

Characteristic Line K3 in FIG. 5(B) shows particle-diameter of the coalpowder mixed in the starting material of Example 2. As apparent fromcomparison between Characteristic Line K2 and Characteristic Line K3,the pore-diameter of the inorganic porous body formed by the startingmaterial including the coal powder is smaller than particle-diameter ofthe coal powder. This result may be caused by the fact that theinorganic porous body contracts during burning step.

2. Example 3, Example 4

In Example 3, sludge which doesn't include activated carbon powder isutilized as a starting material, and thereby an inorganic porous body isformed on the basis of the method of the First Preferred Embodiment.Particle-diameter distribution of particles of the sludge concerningExample 3 is substantially the same as results shown in FIG. 1. Also,the composition of sludge working as the starting material, the ignitionloss, and so on are substantially the same as the results shown inTable 1. In Example 3, the burning temperature was 1000° C., the burningtime was 120 minutes, the porosity of the inorganic porous body was 51%.

In Example 4, activated carbon powder is utilized instead of coalpowder. Also, sludge including the activated carbon powder is utilizedas a starting material, and thereby an inorganic porous body is formedon the basis of the method of the Second Preferred Embodiment. As forthe starting material concerning Example 4, activated coalpowder:sludge=1:10 by weight. Thus, a mixture is adjusted to has 20%water.

A grading degree of the activated carbon powder is indicated asCharacteristic Line P3 in FIG. 6(B).

Particle-diameter distribution of particles in the sludge concerningExample 4 is basically the same as that of FIG. 1. Also, the compositionof the sludge working as the starting material, the ignition loss, andso on are the same as those of Table 1. In Example 4, the burningtemperature was 1000° C., the burning time was 120 minutes, the porosityof the inorganic porous body was 69%.

The inventors have measured the pores of inorganic porous body after theburning step in both of Example 3 and Example 4 on the basis of themethod mentioned above.

FIGS. 6 (A) (B) show the measured results. The vertical axis of FIG.6(A) corresponds to that of FIG. 5(A), and the vertical axis of FIG.6(A) corresponds to that of FIG. 5(A). The horizontal axis of FIG. 6(B)corresponds to that of FIG. 5(B), and the horizontal axis of FIG. 6(B)corresponds to that of FIG. 5(B). Characteristic Line M1 in FIG. 6(A)shows pore-volumes cumulated from the small side of pore-diameter in theinorganic porous body concerning the Example 3 in which the sludgeworking as the starting powder doesn't include activated carbon powder.Characteristic Line M2 in FIG. 6(A) shows pore-volumes cumulated fromthe small side of pore-diameter in the inorganic porous body concerningthe Example 4 in which the sludge working as the starting materialincludes activated carbon powder.

Characteristic Line P1 in FIG. 6(B) shows pore-diameter distribution inthe burned inorganic porous body in which the sludge working as thestarting material doesn't include activated carbon powder.Characteristic Line P1 is the same as Characteristic Line K1 in FIG.5(B). As apparent from Characteristic Line P1, the maximum frequencyregion of pores-diameter was 3 to 4 um (micro meters) in the burnedinorganic porous body formed by the starting material which doesn'tinclude activated carbon powder.

Characteristic Line P2 in FIG. 6(B) shows pore-diameter distribution inthe burned inorganic porous body concerning the Example 4 in which thesludge working as the starting material includes activated carbonpowder. As shown by Characteristic Line P2 in FIG. 6(B), the maximumfrequency region of pore-diameter was 1 to 2 um(micro meters) in Example4 in which the starting material includes activated carbon powder.

On the other hand, a dotted line, Characteristic Line P3 shows gradingdistribution of the activated carbon powder used in Example 4.Characteristic Line P3 shows that the maximum frequency region ofpore-diameter was 3 to 10 um (micro meters) in the activated carbonpowder. As understood at Characteristic Line P3 in comparison with theCharacteristic Line P2, the average pore-diameter of the inorganicporous body is smaller than the average particle-diameter of theactivated carbon powder. Probably, the reason is that the inorganicporous body contracts during the burning step.

3. Example 5

In Example 5, sludge, which doesn't include coal powder and activatedcarbon powder, is utilized as a starting material, and thereby aninorganic porous body is formed on the basis of the method of the ThirdPreferred Embodiment. Particle-diameter distribution of particles of thedust concerning Example 5 is the same as results shown in FIG. 2. Also,the composition of the dust working as the starting material, theignition loss, and so on are substantially the same as the results ofNo.2A shown in Table 3. In Example 5, the burning temperature was 1000°C., the burning time was 120 minutes, the porosity of the inorganicporous body was 42%.

The inventors have measured the pores of the burned inorganic porousbody of Example 5 on the basis of the method mentioned above.

FIGS. 7 (A)(B) shows the measured results. The vertical axis of FIG.7(A) corresponds to that of FIG. 5(A), and the vertical axis of FIG.7(A) corresponds to that of FIG. 5(A). The vertical axis of FIG. 7(B)corresponds to that of FIG. 5(B), and the horizontal axis of FIG. 7(B)corresponds to that of FIG. 5(B).

Characteristic Line S1 in FIG. 7(A) shows pore-volumes cumulated fromthe small side of pore-diameter in the inorganic porous body concerningthe Example 5.

Characteristic Line T1 in FIG. 7(B) is a differentiated line ofCharacteristic Line S1, and shows pore-diameter distribution of theburned inorganic porous body. As apparent from Characteristic Line T1 inFIG. 7(B), the maximum frequency area was 10 to 20 um (micro meters) inpore-diameter.

From comparison between FIG. 1 concerning the sludge and FIG. 2concerning the dust, in the inorganic porous body made from the dust, itis assumed that the pore-diameter of the burned inorganic porous bodymay be large, because the average particle-diameter of the dust isconsiderably large the average particle-diameter of the sludge.

4. Strength Test

The inventors have measured strength of the burned inorganic porousbody. In this strength test, an inorganic porous body whosetarget-diameter is 2 mm is placed an upper surface of the horizontaltable capable of rising and falling. Next, the horizontal table is risenat a low speed to press the inorganic porous body against a cage bodydisposed over the horizontal table and to crush the inorganic porousbody. The strength is estimated as a load by which the inorganic porousbody is crushed.

In this strength test, Specimen A corresponds to Example 1, and itexhibits an inorganic porous body made from a starting materialconstituted by the sludge which doesn't include coal powder. Specimen Bcorresponds to Example 5, and it exhibits an inorganic porous body madefrom a starting material constituted by dust including no coal powder.Specimen C corresponds to Example 2, and it exhibits an inorganic porousbody made from a starting material constituted by the sludge mixed withcoal powder.

Further, as an comparable example, Specimen D is constituted by aninorganic porous body made from diatomaceous earth. In Specimen D, theburning temperature was 1000° C. and the burning time was 120 minutes.Also, Specimen D is applied to the strength test similarly.

In addition, as for Specimens A to D, the strength test is carried outin the case where the inorganic porous body is in dried state and in thecase where the inorganic porous body is dampened state by holding thespecimen under water for 24 hours. In the latter case, it is underconsideration that the inorganic porous body is in water-holding statewhen it is utilized in the ground as soil conditioners.

FIG. 8 shows the test results. In FIG. 8, the marks painted in black,such as the blackened circle and the blackened square, exhibit that theinorganic porous body is in dampened state.

In FIG. 8, the marks painted in white, such as the whitened circle andthe whitened square, exhibit that the inorganic porous body is in driedstate. The number of sample in Specimens A to D was twelve respectively.

FIG. 8 shows that the average strength of Specimen A, the averagestrength of Specimen B, the average strength of Specimen C are high.Here, Specimens A to C are concerning the present invention.

On the other hand, the average strength of Specimen D concerning thecomparable example is lower. This may be caused by the fact that aluminacontent is lower in the diatomaceous earth constituting Specimen D.

Moreover, in comparison between Specimens A and C utilizing the sludgeand Specimen B utilizing the dust, Specimens A and C are superior toSpecimen B in the average strength. This may be caused by the fact thatthe sludge is larger than the dust in alumina content as understood fromcomparison between Tables 1 and 2, and the particles of the sludge areminuter than those of the dust.

The strength tests are similarly carried out in case wheretarget-diameter of the inorganic porous body are 4 mm, 6 mm, 10 mm inthe inorganic porous body. Also, the strength test similarly is carriedout in case where the target-diameter of inorganic porous body is morethan 20 mm. In accordance with this results, since the sludge has highalumina content and the particles of the sludge have a smallparticle-diameter, the specimens constituted by the sludge are superiorto the specimens constituted by the dust in the average strength.

                  TABLE 1                                                         ______________________________________                                        Starting Material: Sludge                                                                                         IGNI                                                                          TION  PORO                                SiO.sub.2  Al.sub.2 O.sub.3                                                                      CaO    MgO  FeO  LOSS  SITY                                %          %       %      %    %    %     %                                   ______________________________________                                        BEFORE  60.6   22.4    2.07 2.93 8.27 26.5  --                                BURNING                                                                       AFTER   59.4   23.3    2.35 3.19 7.93  0.1  51.2                              BURNING                                                                       ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Starting Material: Sludge                                                                              IGNITION                                                      SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  CaO                                                                              MgO                                                                              FeO                                                                              LOSS  POROSITY                                                %  %   %  %  %  %     %                                              __________________________________________________________________________    No. 1                                                                            BEFORE                                                                              61.7                                                                             21.8                                                                              2.11                                                                             3.14                                                                             7.67                                                                             24.4  --                                                BURNING                                                                       AFTER 58.9                                                                             23.0                                                                              3.18                                                                             3.33                                                                             7.53                                                                             0.08  48.8                                              BURNING                                                                    No. 2                                                                            BEFORE                                                                              60.7                                                                             22.7                                                                              2.05                                                                             3.11                                                                             7.96                                                                             24.3  --                                                BURNING                                                                       AFTER 60.8                                                                             22.9                                                                              2.18                                                                             3.26                                                                             7.42                                                                             0.12  49.5                                              BURNING                                                                    No. 3                                                                            BEFORE                                                                              61.2                                                                             22.6                                                                              1.97                                                                             3.13                                                                             7.61                                                                             26.0  --                                                BURNING                                                                       AFTER 60.1                                                                             23.7                                                                              2.18                                                                             3.29                                                                             7.23                                                                             0.08  50.3                                              BURNING                                                                    __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        Starting Material: Dust                                                                                          IGNITION                                                                              PORO                               SiO.sub.2 Al.sub.2 O.sub.3                                                                      CaO    MgO  FeO  LOSS    SITY                               %         %       %      %    %    %       %                                  ______________________________________                                        No. 1A                                                                              79.0    10.1    2.4  2.3  3.5  13.6    34                               No. 2A                                                                              79.0    12.0    1.4  1.4  2.5  23.3    42                               ______________________________________                                    

What is claimed is:
 1. A method for producing an inorganic porousbody,using a starting material which has an ignition loss of 20% or moreby weight comprising sludge as a main constituent, said sludge includingsilica and alumina discharged from a casting foundry as sludge-wastes,comprising the steps of: forming a pellet-shaped body or a lump-shapedbody from a mixture obtained by mixing said starting material withwater, and heating said pellet-shaped body or said lump-shaped body at atemperature of at least 800° C. to burn said pellet-shaped body or saidlump-shaped body so as to obtain said inorganic porous body.
 2. Themethod according to claim 1, said sludge includes from 8 to 40% aluminaby weight, and 50% and more silica by weight, except for parts whichcorrespond to the ignition loss.
 3. The method according to claim 1,wherein the mode diameter is in the range of from 0.1 to 20 μm, and themedian diameter is in the range of from 0.1 to 20 μm in particlesconstituting said sludge.
 4. The method according to claim 1, whereinsaid starting material includes carbon-based powder, an averageparticle-diameter of said carbon-based powder being larger than anaverage particle-diameter of particles constituting said sludge.
 5. Themethod according to claim 1, wherein said carbon-containing powder is atleast one material selected from the group consisting of coal powder,activated carbon powder, and graphite powder.
 6. The method according toclaim 4, wherein said inorganic porous body is utilized as a soilconditioner.
 7. A method for producing an inorganic porous body,using astarting material which has an ignition loss of 10% or more by weightcomprising dust as a main constituent, said dust including silica andalumina discharged from a casting foundry as dust-wastes, comprising thesteps of: mixing said starting material with water to make a mixture bymeans of a stirring wing, thereby forming a pellet-shaped body having anon-cylindrical shape, and heating said pellet-shaped body at atemperature of at least 800° C. to burn said pellet-shaped body so as toobtain said inorganic porous body.
 8. The method according to claim 7,wherein said starting material includes carbon-containing powder, anaverage particle-diameter of said carbon-containing powder being largerthan an average particle-diameter of said dust.
 9. The method accordingto claim 7, wherein said carbon-based powder is at least one materialselected from the group consisting of coal powder, activated carbonpowder, and graphite powder.
 10. The method according to claim 1 whereinan average particle-diameter of said carbon-containing powder is in therange of from 2 to 100 μm.
 11. The method according to claim 7, saiddust includes from 9 to 40% alumina by weight, and from 50 to 85% silicaby weight, except for parts which correspond to the ignition loss. 12.The method according to claim 7, wherein the mode diameter is in therange of from 1 to 50 μm, and the median diameter is in the range offrom 1 to 50 μm in particles constituting said dust.
 13. The methodaccording to claim 7, wherein said inorganic porous body is utilized asa soil conditioner.
 14. The method according to claim 1, wherein saidinorganic porous body comprises at least 50% silica by weight and atleast 20% alumina by weight, has a porosity of at least 40% by volumeand comprises pores having 0.1 to 20 μm in pore-diameter.
 15. The methodaccording to claim 1, wherein the pore-diameter is in the range of from1 to 5 μm in said inorganic porous body.
 16. The method according toclaim 1, wherein pores of said inorganic porous body have amountain-shaped distribution in the range of from 0.1 to 20 μm.
 17. Themethod according to claim 1, wherein the porosity of said inorganicporous body is in the range of from 50 to 70%.
 18. The method accordingto claim 1, wherein said pellet-shaped body or said lump-shaped body isformed by stirring said starting material with water by means of astirring wing in a container.
 19. The method according to claim 1,wherein the heating temperature is in the range of from 800° to 1200° C.20. The method according to claim 1, wherein the size diameter ofinorganic porous body is in the range of from 0.1 to 40 mm.
 21. Themethod according to claim 7, wherein said inorganic porous bodycomprises at least 50% silica by weight and at least 20% alumina byweight, has a porosity of at least 40% by volume and comprises poreshaving 0.1 to 20 μm pore-diameter.
 22. The method according to claim 7,wherein said inorganic porous body comprises pores whose pore-diameteris in the range of from 8 to 30 μm.
 23. The method according to claim 7,wherein pores of said inorganic porous body have a pore sizedistribution in the range of from 1 to 60 μm.
 24. The method accordingto claim 7, wherein the porosity of said inorganic porous body is in therange of from 50 to 70%.
 25. The method according to claim 7, whereinthe size diameter of inorganic porous body is in the range of from 0.1to 40 mm.
 26. The method according to claim 7, wherein the heatingtemperature is in the range of from 800° to 1200° C.